AQUATIC EARTHWORMS 637 



may be given here. Specimens intended for sectioning must be 

 kept in water and material which is free from grit until the alimen- 

 tary tract is cleansed from mud and sand. The methods necessary 

 for securing straight and well-extended specimens for fixation vary 

 greatly with the species. Dilute solutions of the fixing agent 

 when of the right strength will often cause the worms to die in a 

 properly extended condition, and this is especially true of some of 

 the Tubificidae when corrosive sublimate is used. Commonly some 

 means of narcotization is required to secure the relaxation neces- 

 sary for the preparation of well-extended specimens. Good re- 

 sults are often obtained by the gradual addition of a solution of 

 chloretone until the worms no longer respond to stimuli and fail 

 to contract excessively when placed in the fixing fluid. Another 

 common expedient used with success for some species is to immerse 

 the worms in water within a closed vessel and there subject them 

 to the action of the vapor of chloroform, which is put into the same 

 closed vessel but in a separate container. Only the vapor should 

 be allowed to reach the water that contains the worms. 



When properly narcotized the specimens may be immersed in 

 the fixing agent and kept straight by holding them against any 

 convenient straight edge until they have become sufficiently rigid. 

 A rectangular glass candy-tray is a convenient vessel for fixation 

 purposes since the angles formed by the sides and the bottom 

 furnish good opportunities for keeping the worms straight. It is 

 often advantageous to use a small amount of fixing fluid at first 

 and to keep the worms only partially submerged until they have 

 become stiffened and then completely immerse them. Small speci- 

 mens like tubificids and enchytraeids may be conveniently fixed on 

 a glass plate with the aid of square-edged toothpicks which have 

 been soaked in the fixing agent. A toothpick with the adhering 

 fluid is placed on the glass, an anesthetized worm stretched along 

 one edge of the toothpick, another toothpick placed against the 

 other side of the worm and a second worm stretched along the free 

 edge of the second toothpick. A repetition of this process will 

 enable one to prepare a considerable number of specimens in a 

 brief time. Subsequent treatment is like that for other material 

 of similar nature. 



